I. Field of the Invention
This invention relates to a cylindrical roller bearing, and more particularly, to a cylindrical roller bearing which is subjected to high speed rotation, and which comprises at least one guide flange arranged in either one or both an outer race and an inner race (ring), the guide face of which slidably receives a pair of adjacent end faces of the cylindrical roller.
II. Description of the Prior Art
Within the art of high speed roller bearings, it is widely known that so-called "skewing" is liable to occur when a cylindrical roller bearing rotates under a radial load.
This phenomenon of skewing will be explained hereinafter by referring to a conventional cylindrical roller bearing.
"Skewing angle" in the following explanation refers to an inclination angle of the axis of the cylindrical roller, relative to the rotating axis of the bearing, when any of the cylindrical rollers rotationally moves around between an inner race and an outer race provided with a pair of annular guide flanges.
A pair of end faces of the cylindrical rollers or roller bearing and guide faces of the flange(s) are, originally, arranged as flat planes, wherein each is normal to the axis of the bearing assembly. Naturally, each end face of the skewed roller makes metal-to-metal contact with a guide face of the guide flange at a point on a circular, radial marginal end of the guide face.
A certain amount of force, due to relative sliding speed and skew moment, will be generated at the point of contact under the relative influence of
(a) the rotational speed of the inner race,
(b) the rotational speed of the cylindrical rollers,
(c) the speed of circular movement of the cylindrical roller revolving around the axis of the bearing and
(d) the skew moment of the cylindrical rollers. The generated force will break the film of lubricating oil between the end faces of the cylindrical rollers and the guide faces of the guide flange when the cylindrical rollers rotate at high speed. Thus, when this occurs there inevitably arises wear between the end face of the rollers and the guide faces of the flange due to metal-to-metal contact.
The kind of wear caused by such skewing, as mentioned above, frequently occurs, for example, in bearings, which receive shafts subjected to high speed rotation at as high as 3,000 r.p.m. This necessarily leads to serious problems, such as, a very short service life of the bearing in use.
In order that detrimental wear of the cylindrical roller bearing can be prevented, it becomes apparent, as can be understood from the causes which bring about the problem, that all three conditions itemized below must concurrently be fulfilled:
(1) lessen the relative sliding velocity at the point of contact,
(2) reduce the amount of force at the point of contact generated by the skew moment, and
(3) ensure that a sufficient lubricant film is maintained at the point of contact.
Each of these conditions will now be considered.
To fulfill condition (1), it is only necessary to shorten the length of the radius of the rotation of the cylindrical roller to less than that at the original contact point. This can be achieved by displacing the contact point away from the radially innermost end of said flange face at its initial position toward a part more adjacent to the raceway surface of the inner race.
The condition of item (2), can be solved by reducing the skewing angle by either:
(a) displacing the point of contact from its position adjacent to the raceway surface toward the radially innermost portion of the guide face of said flange, or
(b) reducing the axial clearance between each end face of the roller and the adjacent guide face of the flange but in such a manner that the amount of axial movement of the roller between the two opposing guide faces and adjacent roller (hereinafter referred to as axial movement) is not excessively small.
The condition of item (3) can be solved by displacing the contact point away from the radially innermost marginal end to the portion more adjacent to the raceway surface, thereby effecting a sort of "wedge"effect.
It is already known, as disclosed in British Pat. No. 1,520,060, that crowning means applied on a guide surface of a flange is effective to prevent the end faces of cylindrical rollers incorporated therein from being in contact with the radially innermost end of the guide faces of the flange. However, this has several drawbacks. Crowning on the guide surface of a flange is very difficult to apply. Furthermore if it can be done, it is still practicably almost unattainable to have a radius of curvature of the guide face of each flange and the requisite amount of axial movement of rollers in each bearing assembly finished with the necessary degree of high accuracy in compliance with the predetermined design dimension. Due to the variations in working, the contact point of the end faces of each roller and the guide flange, even in an assembled roller, differs from one roller to another roller. This renders both the contact point control and the skew angle control very difficult. In this prior art roller bearing, since the amount of axial movement cannot be maintained constant, the nearer the contact point lies to the radially innermost end portion of the guide faces of the flange, the larger the relative sliding velocity becomes.
On the other hand, when the contact point is at a portion nearer to the raceway surface and when the axial movement of the rollers becomes greater, the skew angle of the roller will become greater, and this, naturally, increases the power caused by said skew moment.
Furthermore, where the contact point is at a point near the radially innermost end of guide face and the amount of the axial movement of the rollers is also large, then both the relative sliding velocity and the force generated by skew moment will become so great that they cannot always be compensated by the improved formation of lubricating oil film regardless of the effectiveness of the crowning.
Accordingly, there still remains such drawbacks that all of the aforesaid three conditions cannot concurrently be satisfied by the prior art roller bearings.